The objective of Project III is to further knowledge of the Interrelationship of the risk of human skin cancer and tissue fatty acid biosynthesis, epidermal cell proliferation, and ultraviolet radiation. The proposed case-control study will include 1500 subjects with l) a case group with a recent diagnosis of skin cancer (375 basal cell and 375 squamous cell subjects), and 2) a control group of 750 noncancer subject. The research may facilitate the design of cost effective skin cancer control studies and suggest improved guidelines related to the risk of skin cancer. The study population will be composed of bale and female, Anglo and Hispanic white residents of southern Arizona and provide broad exposure ranges for skin cancer risk factors. Previously identified risk factors will also be evaluated, to control for confounding and measure potential effect modification, including UV exposure, existing actinic keratosis, pigmentation characteristics such as number of nevi, dietary intake, and subcutaneous adipose tissue fatty acid concentrations. Exposure estimates will be based upon structured interview and biochemical assessment of randomly selected population-based cases and control groups. Exposure estimates will be obtained at the initial interview and again 12 months later.